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California Agriculture, Vol. 57, No.2

California soil quality: a closer look
Cover:  Soil is the essential building block for sustainable agriculture and healthy ecosystems. In this issue, UC scientists examine how production agriculture, natural vegetation, and environmental regulation have effected California soil. One study finds that the state's soil has maintained its chemical quality over the last six decades, although erosion appears to have accelerated. Scientists working in oak woodlands report that blue oaks signifcantly enhance the fertility of the soil. Others performing field trials in the Salinas Valley assess the trade-offs of different cultural practices. In addition, researchers provided helpful information to rice growers incorporating rice straw into soil, and to managers seeking to meet environmental regulations while using public lands to graze livestock.
April-June 2003
Volume 57, Number 2

Peer-reviewed research and review articles

Looking back 60 years, California soils maintain overall chemical quality
by Fabrice DeClerck, Michael J Singer
| Full text HTML  | PDF  
Scientists comparing archival soil samples from 1945 to samples collected in 2001 found that soil had maintained chemical quality overall, although there was evidence of accelerated erosion.
To learn whether soil properties important to production agriculture and environmental quality have changed significantly in the past half-century in California, we analyzed archival samples and samples collected in 2001 from the same locations. Comparisons of organic matter content, pH, electrical conductivity, total nitrogen, total carbon and plant-available phosphorus showed significant changes since the mid1900s. Across the state we found increases at the 95% confidence level for plant-available phosphorus, total carbon, pH, and percent clay, and increases at the 90% confidence level for percent silt and total nitrogen. We measured significant decreases at the 95% confidence level for electrical conductivity and percent sand. Based on this sample of 125 soils, we believe that California's soil chemical quality has not decreased significantly over the past 60 years. However, increased clay percentages may be interpreted as a sign of accelerated erosion, which is a sign of decreased soil quality.
Blue oak enhance soil quality in California oak woodlands
by Randy A Dahlgren, William R Horwath, Kenneth W Tate, Trina J Camping
| Full text HTML  | PDF  
Blue oaks create islands of enhanced soil quality and fertility beneath their canopy.
Blue oaks create islands of enhanced soil quality and fertility beneath their canopy. The quality of soil beneath the oak canopy is considerably better than that of the grasslands adjacent to the trees. We found evidence of improved soil quality under blue oaks for physical, chemical and biological soil properties. The type of vegetation (oak versus annual grasses) has a much stronger influence on soil organic matter and nutrient pools than does soil parent material. Removal of oak trees results in a rapid deterioration of soil quality with the majority of the loss occurring within 10 to 20 years after tree removal.
Scientists, growers assess trade-offs in use of tillage, cover crops and compost
by Louise E Jackson, Irenee Ramirez, Ron Yokota, Steven A Fennimore, Steven T Koike, Diane M Henderson, William E Chaney, Karen M Klonsky
| Full text HTML  | PDF  
Use of cover crops and compost increased soil quality in irrigated, intensive production of lettuce and broccoli in the Salinas Valley.
Use of cover crops and compost increased soil quality in irrigated, intensive production of lettuce and broccoli in the Salinas Valley. These methods had the beneficial impacts of increasing soil microbial biomass, increasing total soil carbon and nitrogen, reducing surface bulk density and decreasing the potential for groundwater pollution as a result of nitrate leaching below the root zone. These soil benefits did not lead to lower yields and occasionally resulted in fewer weeds and lower lettuce corky root disease. Although surface minimum tillage reduced yields, it led to reduced potential for nitrate leaching below the root zone. Use of conventional tillage, cover crops, and compost produced high vegetable yields and acceptable net economic returns over a 2-year period, but broccoli was more profitable than lettuce under this regime. Understanding the trade-offs of various costs and benefits will help growers choose management practices that optimize economic and environmental benefits.
Incorporating straw may induce sulfide toxicity in paddy rice
by Suduan Gao, Kenneth K Tanji, Steven C Scardaci
| Full text HTML  | PDF  
Scientists analyzed the causes of sulfide toxicity to rice plants, which has been randomly observed in isolated sites in the Sacramento Valley.
Sulfide toxicity to rice plants has been randomly observed in isolated sites in rice fields and experimental plots in the Sacramento Valley. Plants suffering from sulfide toxicity show signs of retarded growth and reduced yields, including the characteristic blackened roots and, in the most severe cases, death. Because the environmental conditions causing sulfide toxicity are not clear, we carried out a greenhouse pot test. The treatments included straw and sulfate additions to a rice soil to induce sulfide production. Our results contribute to an improved definition of conditions leading to sulfide production, toxicity and impact to rice plants.
Stubble height standards for Sierra Nevada meadows can be difficult to meet
by David F Lile, Kenneth W Tate, Donald L Lancaster, Betsy M Karle
| Full text HTML  | PDF  
New research can help livestock operators develop grazing strategies to meet stubble height standards on public lands throughout the Sierra Nevada.
Standards for the height of herbaceous vegetation remaining in meadows at the end of the growing season have been, and continue to be, implemented on public grazing lands throughout the Sierra Nevada. Although supporting research is limited, stubble height standards are intended to benefit riparian resources by limiting grazing pressure. This study illustrates how the timing and intensity of defoliation in mountain meadows can affect the stubble height of herbaceous vegetation at the end of the growing season, and compares these findings with current standards. The research also can help livestock operators and public lands managers develop grazing management strategies to meet stubble height standards and conduct local applied research to evaluate the appropriateness of general stubble height standards.
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California Agriculture, Vol. 57, No.2

California soil quality: a closer look
Cover:  Soil is the essential building block for sustainable agriculture and healthy ecosystems. In this issue, UC scientists examine how production agriculture, natural vegetation, and environmental regulation have effected California soil. One study finds that the state's soil has maintained its chemical quality over the last six decades, although erosion appears to have accelerated. Scientists working in oak woodlands report that blue oaks signifcantly enhance the fertility of the soil. Others performing field trials in the Salinas Valley assess the trade-offs of different cultural practices. In addition, researchers provided helpful information to rice growers incorporating rice straw into soil, and to managers seeking to meet environmental regulations while using public lands to graze livestock.
April-June 2003
Volume 57, Number 2

Peer-reviewed research and review articles

Looking back 60 years, California soils maintain overall chemical quality
by Fabrice DeClerck, Michael J Singer
| Full text HTML  | PDF  
Scientists comparing archival soil samples from 1945 to samples collected in 2001 found that soil had maintained chemical quality overall, although there was evidence of accelerated erosion.
To learn whether soil properties important to production agriculture and environmental quality have changed significantly in the past half-century in California, we analyzed archival samples and samples collected in 2001 from the same locations. Comparisons of organic matter content, pH, electrical conductivity, total nitrogen, total carbon and plant-available phosphorus showed significant changes since the mid1900s. Across the state we found increases at the 95% confidence level for plant-available phosphorus, total carbon, pH, and percent clay, and increases at the 90% confidence level for percent silt and total nitrogen. We measured significant decreases at the 95% confidence level for electrical conductivity and percent sand. Based on this sample of 125 soils, we believe that California's soil chemical quality has not decreased significantly over the past 60 years. However, increased clay percentages may be interpreted as a sign of accelerated erosion, which is a sign of decreased soil quality.
Blue oak enhance soil quality in California oak woodlands
by Randy A Dahlgren, William R Horwath, Kenneth W Tate, Trina J Camping
| Full text HTML  | PDF  
Blue oaks create islands of enhanced soil quality and fertility beneath their canopy.
Blue oaks create islands of enhanced soil quality and fertility beneath their canopy. The quality of soil beneath the oak canopy is considerably better than that of the grasslands adjacent to the trees. We found evidence of improved soil quality under blue oaks for physical, chemical and biological soil properties. The type of vegetation (oak versus annual grasses) has a much stronger influence on soil organic matter and nutrient pools than does soil parent material. Removal of oak trees results in a rapid deterioration of soil quality with the majority of the loss occurring within 10 to 20 years after tree removal.
Scientists, growers assess trade-offs in use of tillage, cover crops and compost
by Louise E Jackson, Irenee Ramirez, Ron Yokota, Steven A Fennimore, Steven T Koike, Diane M Henderson, William E Chaney, Karen M Klonsky
| Full text HTML  | PDF  
Use of cover crops and compost increased soil quality in irrigated, intensive production of lettuce and broccoli in the Salinas Valley.
Use of cover crops and compost increased soil quality in irrigated, intensive production of lettuce and broccoli in the Salinas Valley. These methods had the beneficial impacts of increasing soil microbial biomass, increasing total soil carbon and nitrogen, reducing surface bulk density and decreasing the potential for groundwater pollution as a result of nitrate leaching below the root zone. These soil benefits did not lead to lower yields and occasionally resulted in fewer weeds and lower lettuce corky root disease. Although surface minimum tillage reduced yields, it led to reduced potential for nitrate leaching below the root zone. Use of conventional tillage, cover crops, and compost produced high vegetable yields and acceptable net economic returns over a 2-year period, but broccoli was more profitable than lettuce under this regime. Understanding the trade-offs of various costs and benefits will help growers choose management practices that optimize economic and environmental benefits.
Incorporating straw may induce sulfide toxicity in paddy rice
by Suduan Gao, Kenneth K Tanji, Steven C Scardaci
| Full text HTML  | PDF  
Scientists analyzed the causes of sulfide toxicity to rice plants, which has been randomly observed in isolated sites in the Sacramento Valley.
Sulfide toxicity to rice plants has been randomly observed in isolated sites in rice fields and experimental plots in the Sacramento Valley. Plants suffering from sulfide toxicity show signs of retarded growth and reduced yields, including the characteristic blackened roots and, in the most severe cases, death. Because the environmental conditions causing sulfide toxicity are not clear, we carried out a greenhouse pot test. The treatments included straw and sulfate additions to a rice soil to induce sulfide production. Our results contribute to an improved definition of conditions leading to sulfide production, toxicity and impact to rice plants.
Stubble height standards for Sierra Nevada meadows can be difficult to meet
by David F Lile, Kenneth W Tate, Donald L Lancaster, Betsy M Karle
| Full text HTML  | PDF  
New research can help livestock operators develop grazing strategies to meet stubble height standards on public lands throughout the Sierra Nevada.
Standards for the height of herbaceous vegetation remaining in meadows at the end of the growing season have been, and continue to be, implemented on public grazing lands throughout the Sierra Nevada. Although supporting research is limited, stubble height standards are intended to benefit riparian resources by limiting grazing pressure. This study illustrates how the timing and intensity of defoliation in mountain meadows can affect the stubble height of herbaceous vegetation at the end of the growing season, and compares these findings with current standards. The research also can help livestock operators and public lands managers develop grazing management strategies to meet stubble height standards and conduct local applied research to evaluate the appropriateness of general stubble height standards.

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